This application is related to Japanese applications Nos. 2000-048806 and 2000-238586, filed on Feb. 25, 2000 and Aug. 7, 2000 whose priorities are claimed under 35 USC xc2xa7 119, the disclosures of which are incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a light transmission device, in particular to a light transmission device provided for AV equipments and optical data transmission devices to allow light transmission by optically coupling an optical fiber cable inserted in an insertion hole of a holder and an optical element held in the insertion hole.
2. Description of Related Art
In recent years, transmission of digital signals through optical communication has been commonly carried out in consumer products. When the product is not used, a protective structure against dust, flux used for assembling a substrate and other foreign objects is provided for an optical/mechanical junction between a light emitting/receiving section of the product and a plug of an optical fiber cable.
FIGS. 8(a) to 9(b) illustrate a schematic structure of a first light transmission device according to the prior art in which a protective cap is utilized as such a protective structure. FIG. 8(a) is a side view and FIG. 8(b) is a front view observed from an open end of a plug insertion hole, both showing the state where the protective cap is inserted (shutter closed state). FIGS. 9(a) is a front view observed from the open end of the plug insertion hole and FIG. 9(b) is a side view, both showing the state where the protective cap is extracted (shutter opened state).
The first light transmission device according to the prior art shown in FIGS. 8(a) to 9(b) includes in a holder 100 an optical element for performing at least either emitting or receiving light. When the device is not used, a protective cap 101 is inserted in a plug insertion hole 12. The protective cap 101 is inserted/extracted along the direction of an arrow described in FIG. 9(b). That is, the plug insertion hole 102 of the light transmission device is completely shut by the protective cap 101 when the device is not used, i.e., when a plug of an optical fiber cable is not inserted in the plug insertion hole 12, so that entering of dust and foreign objects can be prevented.
However, the protective cap 101 requires a projected portion so that one can hold it, which makes the cap larger. Further, the protective cap 101 must be extracted to insert the optical fiber cable and the extracted protective cap 101 must be stored since it has to be re-inserted when the device is not used, which involves a possibility that children might swallow the cap if it is kept in a wrong place.
In connection with the above problem, FIGS. 10(a) to 11(b) schematically show a second light transmission device according to the prior art which does not use the protective cap 101 but employs a shutter 201 which opens outwardly. FIG. 10(a) is a side view and FIG. 10(b) is a front view observed from an open end of a plug insertion hole, both showing the state where the shutter 201 is closed. FIG. 11(a) is a front view observed from the open end of the plug insertion hole and FIG. 11(b) is a side view, both showing the state where the shutter 201 is opened.
The light transmission device includes in a holder 200 an optical element for performing at least either emitting or receiving light. When the device is not used, the plug insertion hole 202 of the light transmission device is shut and protected by the shutter 201. That is, as shown in FIG. 11(b), the shutter 201 is opened/closed along the direction of an arrow Y in accordance with the insertion/extraction of a plug 203a of an optical fiber cable 203 along the direction of an arrow X.
The shutter 201 eliminates the need of extracting the protective cap 101 to insert the optical fiber cable 203. Further, since the shutter 201 is attached to the light transmission device, it is unnecessary to store it and the device is used without any harmful possibilities.
However, the shutter 201 must be opened outwardly by a person to insert the cable 203, which is not so different from the first light transmission device. In some cases, he/she must close the shutter 201 if it remains opened after the plug 203a is extracted. Further, the size of the shutter 201 will be larger because a handle for opening/closing the shutter 201 is required.
FIGS. 12(a) to 13(b) schematically show a third light transmission device according to the prior art which does not use the protective cap 101 but employs a shutter 301 which opens inwardly. FIG. 12(a) is a sectional side view and FIG. 12(b) is a front view observed from an open end of the plug insertion hole, both showing the state where the shutter is closed. FIG. 13(a) is a front view observed from the open end of the plug insertion hole and FIG. 13(b) is a sectional side view, both showing the state where the shutter is opened.
The third light transmission device includes in a holder 300 an optical element 304 for performing at least either emitting or receiving light. When the device is not used, a plug insertion hole 302 of the light transmission device is shut and protected by the shutter 301.
In this construction, a spring 305 having a pair of arms is provided with a pivot 306. One of the arms contacts a rear surface of the shutter 301 and the other contacts an upper inner surface of the holder 300, so that the shutter 301 automatically opens/closes by turning about the pivot 306 in accordance with the insertion/extraction of a plug 303a of an optical fiber cable 303.
That is, the shutter 301 is closed so as to shut the plug insertion hole 302 when the device is not used. By pressing the plug 303a against the shutter 301, the shutter 301 turns about the pivot 306 to open towards the inside of the holder 300. When the plug 303a is extracted, the shutter 301 automatically returns to its original place by the returning force (elastic force) of the spring 305.
Thus, disadvantages of the second light transmission device, i.e., the need of manual opening and closing of the outwardly opening shutter 201 and the increase of its size, are eliminated.
However, the third light transmission device has the following problems unsolved.
The above-illustrated plug 303a of the optical fiber cable 303 is in a cube shape and a pair of belt-shaped projections (engaging projections) each having a semicircle section is provided (303b in FIG. 13(b)). Further, as shown in FIGS. 14(a) and 14(b), a pair of grooves 307 (engaging grooves) each having a semicircle section is provided in the opposite inner walls of the plug insertion hole 302 of the light transmission device to engage with the projections 303b. FIGS. 14(a) and 14(b) are front views observed from an open end of the plug insertion hole of the third transmission device, showing the state where the shutter is closed and opened, respectively.
The projections 303b are engaged with the grooves 307 to insert the plug 303a to a desired position so that the optical element 304 accommodated in the holder 300 and an edge of the plug 303a of the optical fiber cable 303 where light is emitted (or received) are optically coupled.
The plug 303a is inserted in the plug insertion hole 302 of the holder 300 until the edge thereof contacts the optical element. Therefore, if the optical fiber cable 303 is narrowed as the projections 303b, the edge of the plug 303a and a lens of the optical element are damaged, which deteriorates the optical transmission.
In the third light transmission device, an axis of the spring 305 corresponds to the pivot 306 of the shutter 301 as shown in FIGS. 15(a) and 15(b). Further, as shown in FIG. 13(a), a part of the shutter 301 covering the pivot 306 is exposed when viewed from the open end of the plug insertion hole. (FIGS. 15(a) and 15(b) are sectional side views of the third light transmission device. FIG. 15(a) shows the state where the plug 303a is completely inserted and FIG. 15(b) shows the state where the plug 303a is being inserted or extracted in the midway of the plug insertion hole.) Accordingly, if the edge of the plug 303a is pressed against the shutter 301 covering the pivot 306 to insert the plug 303a, excessive load is applied to the pivot 306, which may possibly break the pivot 306.
To solve the above-mentioned problems, the present invention provides a light transmission device capable of strictly preventing dust and foreign objects from entering the plug insertion hole, without using the protective cap which must be stored when extracted.
According to the present invention, provided is a light transmission device comprising an optical fiber cable having a plug and a holder having a plug insertion hole into which the plug of the optical fiber cable is inserted, the holder containing an optical element exposed in the plug insertion hole for performing at least either emitting or receiving light so that the plug inserted in the plug insertion hole is optically coupled with the optical element, wherein an engaging projection is provided on an outer surface of the plug, an engaging groove corresponding with the projection is provided on a wall of the plug insertion hole, and a shutter for closing the plug insertion hole is provided, the shutter being opened and closed in the inside of the plug insertion hole by turning about a pivot extending substantially vertically or parallel to a line composed of an optional point in the groove and a point on a wall of the plug insertion hole rightly opposite to the optional point.
In the thus constructed light transmission device, the shutter is opened and closed in the inside of the plug insertion hole by turning about a pivot extending substantially vertically or parallel to the line composed of an optional point in the groove and a point on the wall of the plug insertion hole opposite to the optional point. Accordingly, the plug insertion hole is covered with the shutter and thus strictly protected from dust and other foreign objects without using the protective cap used in the prior art devices.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.